The invention concerns a device for ignition delay for electrically-operated ammunition, especially decoy flare ammunition with pyrotechnic, pyrophoric or hypergolic active masses.
For the defence from guided missiles with infrared homing heads, aircraft are served, inter alia, with pyrotechnic infrared emitters, so-called flares. These flare ammunitions generally consist of a cartridge case with electrical ignition device and pyrotechnic active mass. Cartridges for decoy flare ammunition are available in many calibers. Thus, there are cylindrical ammunitions with the calibers 26.5, 36,, 38, 40 and 55 mm. Furthermore, there are ammunitions with rectanguler cross-section with the calibers 25xc3x9725, 25xc3x9752 and 52xc3x9765 mm. As active masses, there are frequently used charges based on magnesium/Teflon/viton or based on red phosphorus, furthermore pyrophoric and hypergolic active masses are known. Characteristic for all flare active masses is the strong heat development and flame formation occurring in the case of the burning up.
For use-tactical reasons, the maximum heat development in the case of the use of flares must, after the discharge, be achieved as near as possible to the aircraft. This means that the active mass already a few decimeters after the discharge from the cartridge case must have achieved its greatest reaction speed in order to ensure the optimum protection effect.
In order to achieve this objective, it would now be logical to ignite the active mass similarly as in the case of pyrotechnic signal ammunition directly within the cartridge case with the help of the propellent. However, against this process speaks the danger of the damaging and destruction of the discharge device or even of the aircraft due to the most very vigorous burning off of the active mass already in the discharge device.
In order to prevent such a premature burning off of the active mass in the discharge device, one uses so-called tubular fuses. These devices ensure that the active mass is first ignited outside of the discharge device.
Examples for such tubular fuses are e.g. slider safeguarding, such as is described e.g.. in U.S. Pat. No. 5,561,259. The principle of this safeguarding is based on the fact that, by the burning off of the propellant, a pyrotechnic delaying element (VZ element) is initiated in a propulsion reflector. If the propulsion reflector reaches outside of the cartridge case, then, by means of spring power, the ignition canal between VZ element and active mass-sided igniter is freed and the ignition of the active mass takes place. If, for example, the propellant is too weak and the active mass and especially the propulsion reflector still remain in the cartridge case, then the ignition canal between the ignited VZ element still remains closed and no initiation of the active mass could occur.
Another form of the tubular fuse provides that, due to the firing acceleration, a mechanical safety device, a so-called g-safety device in a propulsion reflector element is no longer in force. If now this propulsion reflector reaches outside of the cartridge case then, similarly as above described, by means of spring power a stop is removed and a striking pin is released which initiates the active mass via a percussion cap.
The disadvantages of these safety devices consist in that, on the one hand, inert parts of high weight fall to the ground and thus exercises over inhabited grounds are inadmissible. On the other hand, in the case of joint flights, the danger exists that these parts can get into the driving systems of other machines and, in the extreme case, the affected driving system can break down.
A special disadvantage of the last-mentioned tubular fuses consists in the danger of an unintended initiation in the case of the production of such ammunition. Thus, only a small acceleration loading suffices in order to place the g-safety device out of action and to remove the safety of the striking pin for the initiation of the percussion cap where-by, after removal of the active material body from the cartridge case, it come to the firing of the active mass.
Another tubular fuse already long since known and in use functions via a frictional element. By means of a propellant, the active mass body is thereby pushed from the cartridge via the propulsion reflector. On the cartridge mouth, a subcaliber tapering ensures that the propulsion reflector is securely held. On the other hand, because of the acceleration, the active mass moves further and separates from the propulsion reflector. A frictional wire fixed on the propulsion reflector is, therefore, pulled by a frictional detonating cap integrated in the active mass and brings about the initiation of the active mass (decoy flare MJU-8A/B).
In the case of this technical solution, no inert parts are ejected since the propulsion reflector remains in the cartridge and the detonating cap burns off with active body. However, of considerable disadvantage is the high mechanical sensitivity of the friction element. Thus, in the past many accidents have occurred in the case of the transport, loading and discharging of these ammunitions.